1. Field of the Invention
This invention relates to a gas laser having an improved discharge tube.
2. Description of the Prior Art
In general, gas laser include a pair of electrodes, for example a cathode and an anode, within a discharge tube. When a DC power supply connected between the cathode and the anode is energized, there occurs glow discharge between both electrodes and a gas mixture such as carbon dioxide (CO.sub.2), nitrogen gas (N.sub.2) or helium (He) filled in the discharge tube is excited with energy of the glow discharge to the population invertion state, so that a laser beam is generated. The laser beam is reflected by a reflecting mirror and an output mirror which are disposed at both ends of the discharge tube, respectively, so as to go and return therebetween. A part of the thus amplified laser beam is output to the outside through the output mirror.
It is already known that laser output per unit length of the discharge tube can be increased by cooling the gas mixture which has been warmed up during glow discharge. A typical cooling means comprises a cooling passage in communication with the discharge tube, and a heat exchanger and a blower are disposed in the cooling passage. The gas mixture is forcedly fed into the cooling passage from the discharge tube, cooled with the heat exchanger and then, circulated to pass through the discharge tube once again. On this occassion, a speed of the running gas mixture reaches above 10 m per second.
On the other hand, when focusing the led out laser beam by means of a lens or the like, the maximum energy density is observed on is focal plane in the so-called single mode where distribution of the intensity of the laser beam assumes the gauss distribution. In the case the laser beam in single mode is used to machine workpieces, particularly used for froming grooves or openings in steel plates, it is possible to render the groove with a narrower width and the openings with a smaller diameter, so that such laser beam can perform precise machining. In order to generate a laser beam in single mode, there is usually adopted such a means as reducing an inner diameter of the discharge tube or increasing a distance between the mirrors at both ends of the tube. In addition, there is also adopted such a method for generating a laser beam in single mode and with higher output that a number of discharge tubes of a small diameter are employed and these discharge tubes are optically coupled to each other using a number of mirrors.
However, the above described increase in a total length by the use of plural discharge tubes or reduction in an inner diameter of the discharge tube is inevitably accompanied with the fact that the resistance exerted on the gas mixture when passing through the discharge tube, that is, a pressure loss within the discharge tube is increased correspondingly. Therefore, such a blower was required for the conventional gas laser which can produce a large pressure enough to overcome the increased pressure loss.
Also, the increase in a total length by the use of plural discharge tubes connected to each other requires a larger space for installation thereof. With a view to avoid enlargement in a length of the discharge tube, Japanese Patent Open to the Public No. 49-64392 proposes a gas laser in which cooling cylinders 31 to 34 and discharge cylinders 21 to 24 are disposed within a hollow tube 1. But the gas laser shown in FIG. 2 has such a construction that a plurality of laser beams are led out and these beams are focused on a point, thus inevitably leading to a difficulty in focusing and more complicated structure.